425 research outputs found
Light-Hierarchy: The Optimal Structure for Multicast Routing in WDM Mesh Networks
Based on the false assumption that multicast incapable (MI) nodes could not
be traversed twice on the same wavelength, the light-tree structure was always
thought to be optimal for multicast routing in sparse splitting Wavelength
Division Multiplexing (WDM) networks. In fact, for establishing a multicast
session, an MI node could be crosswise visited more than once to switch a light
signal towards several destinations with only one wavelength through different
input and output pairs. This is called Cross Pair Switching (CPS). Thus, a new
multicast routing structure light-hierarchy is proposed for all-optical
multicast routing, which permits the cycles introduced by the CPS capability of
MI nodes. We proved that the optimal structure for minimizing the cost of
multicast routing is a set of light-hierarchies rather than the light-trees in
sparse splitting WDM networks. Integer linear programming (ILP) formulations
are developed to search the optimal light-hierarchies. Numerical results
verified that the light-hierarchy structure could save more cost than the
light-tree structure
Optical Multicast Routing Under Light Splitter Constraints
During the past few years, we have observed the emergence of new applications
that use multicast transmission. For a multicast routing algorithm to be
applicable in optical networks, it must route data only to group members,
optimize and maintain loop-free routes, and concentrate the routes on a subset
of network links. For an all-optical switch to play the role of a branching
router, it must be equipped with a light splitter. Light splitters are
expensive equipments and therefore it will be very expensive to implement
splitters on all optical switches. Optical light splitters are only implemented
on some optical switches. That limited availability of light splitters raises a
new problem when we want to implement multicast protocols in optical network
(because usual multicast protocols make the assumption that all nodes have
branching capabilities). Another issue is the knowledge of the locations of
light splitters in the optical network. Nodes in the network should be able to
identify the locations of light splitters scattered in the optical network so
it can construct multicast trees. These problems must be resolved by
implementing a multicast routing protocol that must take into consideration
that not all nodes can be branching node. As a result, a new signaling process
must be implemented so that light paths can be created, spanning from source to
the group members
A multipopulation parallel genetic simulated annealing based QoS routing and wavelength assignment integration algorithm for multicast in optical networks
Copyright @ 2008 Elsevier B.V. All rights reserved.In this paper, we propose an integrated Quality of Service (QoS) routing algorithm for optical networks. Given a QoS multicast request and the delay interval specified by users, the proposed algorithm can find a flexible-QoS-based cost suboptimal routing tree. The algorithm first constructs the multicast tree based on the multipopulation parallel genetic simulated annealing algorithm, and then assigns wavelengths to the tree based on the wavelength graph. In the algorithm, routing and wavelength assignment are integrated into a single process. For routing, the objective is to find a cost suboptimal multicast tree. For wavelength assignment, the objective is to minimize the delay of the multicast tree, which is achieved by minimizing the number of wavelength conversion. Thus both the cost of multicast tree and the user QoS satisfaction degree can approach the optimal. Our algorithm also considers load balance. Simulation results show that the proposed algorithm is feasible and effective. We also discuss the practical realization mechanisms of the algorithm.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/1, the National Natural Science Foundation of China under Grant nos. 60673159 and 70671020, the National High-Tech Research and Development Plan of China under Grant no. 2006AA01Z214, Program for New Century Excellent Talents in University, and the Key Project of Chinese Ministry of Education under Grant no. 108040
Avoidance of multicast incapable branching nodes for multicast routing in WDM networks
In this articlewestudy themulticast routing problem in all-opticalWDMnetworks
under the spare light splitting constraint. To implement a multicast session,
several light-trees may have to be used due to the limited fanouts of network
nodes. Although many multicast routing algorithms have been proposed in order
to reduce the total number of wavelength channels used (total cost) for a
multicast session, the maximum number of wavelengths required in one fiber link
(link stress) and the end-to-end delay are two parameters which are not always
taken into consideration. It is known that the shortest path tree (SPT) results
in the optimal end-to-end delay, but it can not be employed directly for
multicast routing in sparse light splitting WDM networks. Hence, we propose a
novel wavelength routing algorithm which tries to avoid the multicast incapable
branching nodes (MIBs, branching nodes without splitting capability) in the
shortest-path-based multicast tree to diminish the link stress. Good parts of
the shortest-path-tree are retained by the algorithm to reduce the end-to-end
delay. The algorithm consists of tree steps: (1) aDijkstraPro algorithmwith
priority assignment and node adoption is introduced to produce a SPT with up to
38% fewer MIB nodes in the NSF topology and 46% fewerMIB nodes in the USA
Longhaul topology, (2) critical articulation and deepest branch heuristics are
used to process the MIB nodes, (3) a distance-based light-tree reconnection
algorithm is proposed to create the multicast light-trees. Extensive
simulations demonstrate the algorithm's efficiency in terms of link stress and
end-to-end delay
Hypo-Steiner heuristic for multicast routing in all-optical WDM mesh networks
International audienceIn sparse light splitting all-optical WDM networks, the more destinations a light-tree can accommodate, the fewer light-trees andwavelengths amulticast session will require. In this article, a Hypo-Steiner light-tree algorithm (HSLT) is proposed to construct a HSLT light-tree to include as many destinations as possible. The upper bound cost of the light-trees built by HSLT is given as N(N â1)/2, where N is the number of nodes in the network. The analytical model proves that, under the same condition, more destinations could be held in a HSLT than a Member-Only (Zhang et al., J. Lightware Technol, 18(12), 1917â1927 2000.) light-tree. Extensive simulations not only validate the proof but also show that the proposed heuristic outperforms the existing multicast routing algorithms by a large margin in terms of link stress, throughput, and efficiency ofwavelength usage
Resilient optical multicasting utilizing cycles in WDM optical networks
High capacity telecommunications of today is possible only because of the presence of optical networks. At the heart of an optical network is an optical fiber whose data carrying capabilities are unparalleled. Multicasting is a form of communication in wavelength division multiplexed (WDM) networks that involves one source and multiple destinations. Light trees, which employ light splitting at various nodes, are used to deliver data to multiple destinations. A fiber cut has been estimated to occur, on an average, once every four days by TEN, a pan-European carrier network. This thesis presents algorithms to make multicast sessions survivable against component failures. We consider multiple link failures and node failures in this work. The two algorithms presented in this thesis use a hybrid approach which is a combination of proactive and reactive approaches to recover from failures. We introduce the novel concept of minimal-hop cycles to tolerate simultaneous multiple link failures in a multicast session. While the first algorithm deals only with multiple link failures, the second algorithm considers the case of node failure and a link failure. Two different versions of the first algorithm have been implemented to thoroughly understand its behavior. Both algorithms were studied through simulators on two different networks, the USA Longhaul network and the NSF network. The input multicast sessions to all our algorithms were generated from power efficient multicast algorithms that make sure the power in the receiving nodes are at acceptable levels. The parameters used to evaluate the performance of our algorithms include computation times, network usage and power efficiency. Two new parameters, namely, recovery times and recovery success probability, have been introduced in this work. To our knowledge, this work is the first to introduce the concept of minimal hop cycles to recover from simultaneous multiple link failures in a multicast session in optical networks
Multicast routing from a set of data centers in elastic optical networks
This paper introduces the Multi-Server Multicast (MSM) approach for Content Delivery Networks (CDNs) delivering services offered by a set of Data Centers (DCs). All DCs offer the same services. The network is an Elastic Optical Network (EON) and for a good performance, routing is performed directly at the optical layer. Optical switches have heterogeneous capacities, that is, light splitting is not available in all switches. Moreover, frequency slot conversion is not possible in any of them. We account for the degradation that optical signals suffer both in the splitting nodes, as well as across fiber links to compute their transmission reach. The optimal solution of the MSM is a set of light-hierarchies. This multicast route contains a light trail from one of the DCs to each of the destinations with respect to the optical constraints while optimizing an objective (e.g., minimizing a function). Finding such a structure is often an NP-hard problem. The light-hierarchies initiated from different DCs permit delivering the multicast session to all end-users with a better utilization of the optical resources, while also reducing multicast session latencies, as contents can be delivered from such DCs closer to end-users. We propose an Integer Linear Programming (ILP) formulation to optimally decide on which light-hierarchies should be setup. Simulation results illustrate the benefits of MSM in two reference backbone networks.Peer ReviewedPostprint (author's final draft
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